1. Field of the Invention
This invention relates to a blood leak detector and more particularly to a detector which passes light through a sample solution and indicates the ratio of light passing through the sample at frequencies of high blood absorption to light passing through the sample at frequencies of low blood absorption.
2. Description of the Prior Art
In a number of known clinical systems, such as hemodialysis systems, it is desirable and sometimes necessary to detect the presence of small amounts of blood in a clinical solution. In the hemodialysis system, for example, the presence of blood in the salt solution utilized for dialysis indicates leakage through the dialyzer membrane or some other point in the system. Leakage in a very small proportionality (e.g. concentrations from 0.25 to 7.0 mg % of hemoglobin (hb)) must be detected in order to sound an alarm to indicate a system malfunction.
Known blood leak detection systems typically operate in response to the difference between a sample reading that is responsive to turbidity of the solution, and a reference reading which represents the average broadband light output of the lamp source. Using the broadband or some other average characteristic of the light source as a reference, the different reading provided by the turbidity-responsive sampling provides a signal indicating the presence of hemoglobin in the blood. However, contamination of the windows in the optical path or any source of turbidity which usually collects during the course of dialysis tends to diminish the reading channel intensity, substantially affecting the accuracy of the measurement that is provided. Similarly, the presence of other turbidity than hemoglobin can effect the reference level, as can the light output of the illuminating source, which tends to diminish with aging of the lamp. It is possible to compensate, at extra expense, for lamp aging effects and for other reference signal variations by servo techniques which, for example, increase lamp energization current in order to tend to maintain a constant illumination output. However, it is still not feasible to provide a highly sensitive output that is relatively unaffected by contamination and turbidity effects.
Other problems in known systems relate to automatic response to alarm conditions. On a typical blood dialysis system the dialyzer must be bypassed and the detector flushed upon the detection of blood. However, flushing of the detector eliminates the alarm condition to cause the system to oscillate between normal and alarm operation modes. In at least one system that is protected against oscillation, it is extremely difficult to restart normal operation once an alarm condition is detected.